1. Field of the Invention:
This invention relates to gas laser systems and more particularly to pre-ionization electrodes within the plasma chambers. The invention is embodied in a sealed nitrogen gas laser having a pair of capacitance coupled, symmetrically positioned pre-ionizing elements.
2.Description of the Prior Art:
Many gas lasers require a constant recirculation of gases during operation because of deterioration or changes in the gas during operation. Sealed plasma chambers have also been used, but in general such sealed plasma chambers using either atomic or molecular gases have a shorter life than those with a continual supply of fresh gas.
High power lasers utilize plasma chambers formed of materials such as ceramic and quartz because of the high temperatures associated with such lasers. In lower power laser systems using relatively inert gases, such as nitrogen, it is usual practice to form the plasma chambers from plastic. This choice is made because plastic is more readily shaped and machined and does not break easily. Since the gas is not reactive and high temperatures are not produced during operation, there is no obvious reason for using materials that are more difficult to fabricate, such as ceramic and quartz. However, nitrogen gas lasers heretofore constructed have an acceptable life only if periodically replenished with fresh gas. No satisfactory nitrogen gas laser has been constructed using a sealed plasma chamber.
Gas lasers have been provided with various kinds of pre-ionizer elements in the forms of shields and screens or spark sources. These pre-ionizer elements are not well suited for small low-power gas lasers, resulting in some instances in the requirement for separate high voltage switches, pulse generating means and synchronizing circuits. Excessive ionization currents and perturbation of the laser beam are frequent sources of difficulty.
Many gas lasers previously in use are satisfactory only for laboratory applications because of the requirement for a steady flow of fresh gas or because considerations of cost or complexity make commercial use impracticable.
U.S. Pat. No. 4,380,079 to Cohn et al shows a laser having a pre-ionizing electrode which creates a series of spark discharges along the length of the electrode. A similar pre-ionizing system is described in a thesis entitled "Far Infrared Spectroscopy of Methyl Alcohol using Continuously-Tunable TEA Laser Optical Pumping", submitted to Massachusetts Institute of Technology in June 1979 by Robert G. Gibson in partial fulfillment of the requirements for the Degree of Doctor of Philosophy. The pre-ionizer element is typical of previously used pre-ionizers. Those pre-ionizers are not effective in eliminating streamers and preventing perturbation of the main discharge and thus fail to provide maximum laser performance.